Intra-breath respiratory oscillometry in the first days of life in preterm infants: a prospective observational study.

UNLABELLED: We aimed to describe intra-breath changes in respiratory system resistance (Rrs) and reactance (Xrs) in preterm infants receiving non-invasive respiratory support during the first days of life. This prospective observational study included infants born at < 32 weeks' gestation. Respiratory oscillometry was performed at 24-48 h of life using a ventilator that superimposed sinusoidal oscillations (10 Hz) on a continuous positive airway pressure of 5 cmH2O. We calculated the average Rrs and Xrs over inspiration (Rinsp and Xinsp) and expiration (Rexp and Xexp), end-inspiratory and end-expiratory Rrs (Rei and Ree), and Xrs (Xei and Xee). We included 69 infants. Rexp was higher than Rinsp (median (IQR) = 42.91 (33.80, 56.94) vs 39.36 (31.61, 47.08) cmH2O·s/L, p < 0.001); Xexp was lower than Xinsp (- 27.63 (- 47.76, - 19.58) vs - 27.51 (- 38.74, - 19.79) cmH2O·s/L, p = 0.013). Ree was lower than Rei (41.46 (32.25, 52.26) vs 38.92 (30.99, 47.18) cmH2O·s/L, p < 0.001); Xei was lower than Xee - 28.07 (- 42.12, - 21.84) vs - 24.56 (- 37.81, - 17.65) cmH2O·s/L, p < 0.001). Gestational age significantly explained all intra-breath fluctuations in oscillatory mechanics. The deterioration in Xexp relative to Xinsp showed high inter-subject variability. It was associated with poor lung compliance (inspiratory Xrs z-score), even after adjusting for gestational age (beta (SE) = 0.93 (0.39), p = 0.020). CONCLUSION: Preterm infants exhibit changes in intra-breath oscillatory mechanics, especially at low gestational age. The reduction in Xrs during expiration is associated with reduced lung compliance and may reflect compensatory mechanisms that elevate end-expiratory lung volume. WHAT IS KNOWN: • Intra-breath changes in oscillatory mechanics have been used to reveal disease-specific pathophysiological behaviours in other age groups. WHAT IS NEW: • This study shows that intra-tidal changes in oscillatory mechanics are present in preterm infants on nasal continuous positive airway pressure during the first days of life and may reflect compensatory mechanisms that dynamically elevate lung volume in infants with poor lung compliance. • This study has implications for the standardisation of the methodology to apply respiratory oscillometry in preterm infants.